<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>CSS选择器</title>
  <style>
      div{
       background-color: aqua;
      }
      #div1{
          color: brown;
      }
      .span{
         font-size: 30px;
      }

  </style>
</head>
<body>

    <div id="div1">div1</div>
    <div id="div2">div2</div>
    <div id="div3">div3</div>
    <span id="4" class="span">span1</span>
    <span id="5" class="span">span2</span>
    <span id="6" class="span">span3</span>
</body>
</html>